A CHESS (Chemical Shift Selective) method is known as one of fat suppressing techniques (techniques of drawing a desired tissue with high contrast by using the difference in chemical shift of proton among tissues) of MRI. According to the CHESS method, protons of a fat tissue are selectively excited by high-frequency magnetic field pulses of 90° having the resonance frequency of the protons of the fat tissue (hereinafter referred to as CHESS pulses), for example, and then a spoil pulse is applied so that transverse magnetization of the excited protons of the fat tissue is subjected to phase dispersion. Thereafter, a normal imaging pulse sequence is executed to measure a signal from only water protons.
However, the fat suppressing technique using the CHESS pulse has a problem that when the irradiation magnetic field based on the CHESS pulse has spatial non-uniformity, non-uniformity occurs in the exciting state of protons of a fat tissue as a suppression target and there occurs an area in which the fat suppression is insufficient.
A conventional technique disclosed in Patent Document 1 is known as a conventional technique to solve this problem. According to the conventional technique described in Patent Document 1, it is disclosed that the effect of the non-uniformity is reduced by applying plural CHESS pulses at different flip angles.
Patent Document 1: JP-A-7-289534
However, as a result of studies of the above conventional technique, the inventor has found the following problem. That is, the Patent Document 1 discloses that plural CHESS pulses are applied to reduce the effect of the spatial non-uniformity of the CHESS pulse itself, however, it has not specifically disclosed any technique of optimizing the flip angle and the application interval of the CHESS pulses.